The 3rd Generation Partnership Project (3GPP) recently added support for the Earthquake and Tsunami Warning System (ETWS) to existing wireless communication standards, including the GSM/EGPRS standards. These new changes enable subscribers to receive warning messages and other notifications in response to ETWS events. Two types of notifications are transmitted to subscribers in response to an ETWS event. A primary notification (PN) is transmitted in order to quickly inform and warn subscribers about an earthquake or tsunami that will affect the subscriber's current geographic area. The goal is to provide primary notification within four seconds of an ETWS event. The secondary notification is transmitted to provide supplementary information about the ETWS event, such as where to get assistance and where to find refuge or shelters, and how to get food or medical assistance.
In GSM/EDGE mobile networks, different methods of transmitting the primary notification message may be used, depending on the state of the mobile terminal (also known as a user terminal). For example, a mobile station in idle mode may receive the primary notification message in a paging message transmitted on a paging channel. Depending on the length of the primary notification message, the primary notification message may be segmented and inserted into two or more paging messages. Therefore, the mobile terminal needs a mechanism to identify the segments belonging to the same primary notification message and the proper order of the segments in order to reassemble the primary notification message.
Because the mobile terminal may receive the PN segments out of order, there is some risk that a mobile terminal may attempt to reassemble a PN message using PN segments from two different PN messages. This situation may occur, for example, when transmission of a first PN message is aborted and replaced by a second PN message. If the mobile terminal has not received all of the segments of the first PN message, it may try to use PN segments from the second PN message to complete the first PN message. A primary notification message reassemble from segments of different messages will not be valid and the subscriber will not be warned. Accordingly, there is a need to provide a mechanism to prevent errors during reassembly of primary notification messages to ensure that the primary notification messages are correctly received by mobile terminals in the mobile communication network.